A conventional chain for transmission or conveyance has a problem that when a tooth flank of a sprocket is engaged with a roller of a chain, noise occurs due to collision of the sprocket and the roller. For example, a technique in which a number of elastic bodies are embedded on the outer face of a bushing of a chain and an impact applied from the tooth flank of a sprocket to the roller is cushioned by the elastic bodies is proposed in Japanese Unexamined Utility Model Publication No. 59-79656.
However, the technique described in the Japanese publication No. 59-79656 has a problem such that since the elastic bodies are protruded from the outer face of the bushing, it is difficult to form an oil film by a lubricating oil and the elastic bodies are quickly worn out.
It is, consequently, considered that the impact is cushioned in the following manner. As shown in FIG. 8, a chain C includes outer plates O, inner plates I, a chain pin P, a bushing B, and a roller R. Oil grooves G which are narrow and long in the axial direction of the bushing B are formed at a plurality of positions in the radial direction on the outer face of the bushing B of the chain C. A portion between the bushing B and the roller R is filled with a lubricating oil L in a state where the lubricating oil L is stored in the oil grooves G. When the roller R collides with the tooth flank of a sprocket (not shown) and is impacted, the impact is cushioned by a wedge or squeeze effect of the lubricating oil L interposed between the bushing B and the roller R.
However, in the chain C with such a construction, the outer face of the bushing B is deformed to a barrel shape, i.e., bulging outward in the middle (hereinlater, simply called a barrel shape), in an assembling step of press-fitting both ends of the bushing B to bushing holes H of the inner plates I. Consequently, a clearance S between the inner face of the roller R and the outer face of the bushing B is widened near both ends of the roller R having the cylindrical inner face and the lubricating oil L easily escapes to the outside. The portion between the outer face of the bushing B and the inner face of the roller R enters a mixed or boundary lubrication state, so that the wedge or squeeze effect is not fully shown. Thus, there is a problem that the capability of reducing noise is lowered.
It is, therefore, an object of the present invention to provide a low-noise chain with oil grooves, which solves the problem of the conventional technique and in which a wedging or squeezing effect of a lubricating oil which is interposed between a bushing and a roller is effectively taught, thereby obtaining an excellent effect of noise reduction.